A two-stage gas generator can be seen in the European Patent Application EP-A2 0 502 630. This describes a hybrid gas generator in which after the mechanical opening of a rupture membrane, cold gas flows out from a compressed gas chamber. The first gas-generating stage is therefore a cold gas stage. As a second gas-generating stage, a propellant charge is provided, which is automatically activated by the change in pressure inside the gas generator. This activation takes place by means of a percussion igniter arrangement connected with a reference pressure chamber.
A disadvantage of the arrangement according to EP-A2 0 502 630 is that this arrangement must compulsorily operate at a reference pressure, which corresponds approximately to the pressure in the compressed gas chamber. A simple adaptation of the generated gas volume is not possible by simple means, in particular not by reducing the pressure inside the gas generator without adapting the reference pressure. The mechanical ignition arrangement provided for the second gas-generating stage is extremely costly, requires several movable parts and the arrangement of striker and percussion igniter, in particular when filling the gas generator, represents a considerable safety risk, because an accidental activation of the percussion igniter can not be absolutely ruled out.
It is an object of the invention to provide a gas generator which makes possible an activation of the second gas-generating stage as a function of a pressure change in the gas generator, however independently of the extent of the pressure inside the gas generator.